Automated clutches or clutches actuated by an actuator are increasingly finding application in modern motor vehicles. The reliability of actuation of such clutches is accorded decisive importance, not only for reasons of convenience but rather also from the viewpoint of safety.
From DE 102 35 386 A1 a process for controlling a gear actuator mechanism with a clutch actuator and a control device for an automated clutch is known, wherein the clutch actuator is controlled as a function of certain operating states in such a manner that situations critical to safety are avoided. For example, in a process of shifting into gear during startup a reduction in force and/or speed can be caused by actuation of the actuator. To recognize stops of the gear gates a suitable algorithm can be provided. Furthermore, a faulty turning direction of the motor can be recognized and/or corrected. The position of the clutch can be controlled with the aid of the curve of momentum.
Often, clutches are used which automatically assume their open position in case of a fault in the actuation system, so that, for example, unintentionally putting the vehicle in motion is avoided. In the case of parallel shift gearboxes or twin-clutch transmissions it is absolutely necessary that the two clutches assume their respective open state reliably. Such twin-clutch transmissions comprise two sub-transmissions with which one shifts into different gears. If, for example, one shifts into the even gears with one sub-transmission and into the odd gears with another sub-transmission, when a gear is engaged the clutch assigned to the transmission with odd gears must be open if the clutch assigned to the sub-transmission with even gears is closed and, for example, one is driving in second gear. In the sub-transmission with the odd gears, with an open clutch an odd gear can then be pre-engaged where shifting into this gear is accomplished merely by closing the clutch of the transmission with the odd gears and opening the clutch of the sub-transmission with the odd gears. If in both sub-transmissions a gear is engaged and both clutches are closed, this would lead to the destruction of the transmission. Accordingly, clutches of parallel shift gearboxes are preferably constructed in such a manner that they are pressed into the closed position by an actuator against the force of an opening spring and are moved into the open position by the closing spring as soon as the actuator is no longer energized with energy for closing the clutch.
If, in such clutches impelled into the closed position, the restoring force of the opening spring is no longer sufficient to move an actuation element back into its initial position, the clutch would not open completely even if no more actuation force into the closed position were applied. Causes for this can, for example, include wear in the actuation mechanism, corrosion, or other impacts.